Dua e Tawassul is the name of several Duas; But a Dua with the same name is more famous, the source of which is the book of Biharulanvar. Allama Majlisi found this prayer in one of the old versions and in that book it is stated that this Dua was narrated by Muhammad ibn Babwaih Qommi from the Imams (AS) and it will be answered immediately for everything.
Tawassul in the teachings of the Shiites and the majority of Muslims means relying on a person or thing that has a high status and value in the sight of God, in order to approach him and meet his needs. Tawassul is closely related to the doctrine of intercession, and these two doctrines are usually mentioned together.
Dua e Tawassul" refers to several Duas:
The famous Dua of Tawassul, which begins with the phrase: اللَّهُمَّ إِنِّی أَسْأَلُک وَ أَتَوَجَّهُ إِلَیک
بِنَبِیک نَبِی الرَّحْمَةِ
In Baladul Amin,  Kafami has quoted a detailed Dua called the Dua e Faraj, and at the same time he has mentioned the Dua e Tawassul.
Sayyid Ali Khan has quoted the Dua of Tawassul from Qabs al-Misbah Sheikh Saharashti in Al-Kalama al-Tayyib. 
There is another Dua called Dua e Tawassul in Al-Balad Al-Amin. Kafami introduces this Dua without mentioning the reference, as a Dua narrated from the Imams (AS). In this Dua, the reader of the Dua, in the final verses, swears by the right of the fourteen infallibles, asks God for his needs. 
According to reference, the source of the famous Dua e Tawassul mentioned in Mafatih al-Jannan is the book of Biharul Anvar. This Dua has been narrated by Sheikh Saduq (r.a) from the infallible Imams without referring to the documents and chain of narrations. Allamah Majlisi says: I found this prayer in one of the old manuscripts written by one of our companions and in that book it was said: "This Dua was narrated by Muhammad ibn Babawiyyah Qommi from the Imams (AS) and I recited it for everything immediately was answered. And this is the dua e Tawassul … "
The content of the prayer of supplication is the Dua and request of need from God; with this feature, when we pray, we swear by God to the right of the fourteen infallibles and ask Him to fulfill our need and prayer on their behalf. Such a request is a sign of the position of the saints in the sight of God and has nothing to do with monotheism. 
1. قمی، مفاتیح الجنان، ذیل دعای توسل.
2. ↑ کفعمی، البلدالامین، ۱۴۱۸ق، ص۴۵۲-۴۴۹.
3. ↑ قمی، مفاتیح الجنان، ذیل دعای توسل.
4. ↑ کفعمی، البلدالامین، ۱۴۱۸ق، ص۵۰۳
5. ↑ مجلسی، بحار الانوار، ۱۹۸۳م، ج۹۹، ص۲۴۷.
6. ↑ کاشفى، پرسش و پاسخهای دانشجویی، دفتر چهاردهم، ۱۳۸۳ش، ص۵۹